This invention relates to an improved method for determining the fuel economy which results from the use of fuel efficient carry-over lubricating oils in internal combustion engines. More particularly, this invention involves a method for deconditioning engines used in determining the fuel economy benefits of fuel efficient or friction reducing engine oils wherein a deconditioning oil comprising selected overbased metal salt materials or neutral/normal metal salts in selected amounts is exposed to said engine for a period of time after a candidate oil is tested therein.
In recent years there has been considerable effort to reduce the fuel consumption of internal combustion engines, particularly automotive engines. This has primarily resulted because of the declining sources of petroleum, the rapid escalation in fuel prices and the increasing awareness of energy conservation needs. Many engineering changes have been made to improve fuel economy including more efficient engine systems and car weight reduction through downsizing and expanded use of lightweight materials. While these changes have produced substantial improvements in vehicular fuel economy, additional improvements from other practical sources are still necessary and desirable.
One approach to fuel economy which has recently received considerable attention is the use of lubricants and particularly motor oils which improve fuel economy by reducing the overall friction in the engine and thus result in a reduction of energy requirements. Such so-called "fuel economy" engine oils generally contain friction-reducing or friction-modifying additives.
Along with the introduction of the fuel economy oils came the need for measuring the performance of such oils to determine the actual savings or benefit. This is of particular importance to various industry and government parties interested in assessing or evaluating different types of fuel economy engine oils. Techniques are known for measuring the fuel economy effects of different lubricant oils and generally they involve a comparison of the results obtained with a test oil and a reference oil. While such a procedure may at first seem like a straightforward test operation, it is not that simple since even relatively small variations in some operating conditions can affect the apparent results and thereby obscure the true fuel economy benefits of a test oil.
One problem which has significantly affected the measurement of fuel efficiency for lubricating oils and particularly those containing boundary friction additives is the so-called "carry-over" effect. The carry-over fuel economy effect is defined as an effect characteristic of fuel efficient engine oils whereby these oils condition the engine to produce higher fuel economy which persists for an extended period of operation after the fuel efficient oil has been replaced with a non-fuel efficient oil. In other words it is the residual fuel economy effect imparted by certain lubricating oils. The problem created by the carry-over effect is that it becomes difficult and time consuming to bring a test engine back to a stabilized reference point. However, this is essential if there is to be a meaningful evaluation of different oils.
Accordingly there is the need for a procedure for evaluating the fuel economy effects of lubricating oils in a reasonably quick, efficient manner and particularly overcomes the problem of carry-over which is created by certain oils.